Intersatellite optical communication is expected as an effective bulk communication system in outer space. Since very little light is scattered or absorbed in outer space, outer space is an extremely good light transmission path, which can transmit light for a distance as long as several tens thousands km without the need of amplification.
In order to establish such intersatellite optical communication successfully, optical communication antennas must be set on both of the transmitting and receiving sides to precisely oppose each other with an extremely small limit of error on the order of 1/10,000 degrees. In order to switch a satellite to be communicated with, it is necessary to rapidly track and acquire a target antenna. This means that an optical communication antenna is required to combine high-precision tracking capability and high-speed acquisition capability. In general, a beam pointing system for intersatellite optical communication is composed of two mechanisms of a coarse pointing mechanism (CPM) for roughly controlling the beam direction and a fine pointing mechanism (FPM) for precisely controlling the beam direction on the order of 1/10,000 degrees. Specifically, the CPM is often provided with a large-size gimbal mirror, whereas the FPM is often provided with a small size fast steering mirror. This invention relates to a small size fast steering mirror suitably applicable to the latter, namely the FPM.
This type of beam pointing system is disclosed, for example, in Japanese Laid-Open Patent Publication No. JP-A-2001-264663 (Patent Document 1) and Japanese Laid-Open Patent Publication No. JP-A-H11-281925 (Patent Document 2).
Referring to FIG. 1, a mirror drive mechanism disclosed in Patent Document 1 is of a biaxial gimbal type, and a movable part 249 including a mirror 250 is fixed to a base by means of deformable elastic pivots 246a-246b and 248a-248b. The mirror 250 is tilted about the X-axis and the Y-axis as viewed in the figure by electromagnetic power exerted by a drive unit composed of yokes 245a-245b and 254a-254b, permanent magnets 251a-251b and 252a-252b, and coils 255a-255b and 256a-256b. 
Referring to FIG. 2 and FIG. 3, a laser pointing device 600 disclosed in Patent Document 2 is shown. A mirror holder 602 including a mirror 601 is fixed to a base 605 by means of a torsion bar 603 extending in a Z-axis direction from the center of the mirror holder 602, and a leaf spring 604 which is bent from the XY plane of the mirror holder 602 toward a Z-axis direction. The mirror holder 602 has arms 606 extended therefrom, and there are provided at the ends of the arms, drive units composed of coils 607a to 607d and permanent magnets 608a to 608d, respectively. The mirror holder 602 is tilted by the electromagnetic force of the drive units, toward a θx direction or θy direction around the fixed end of the torsion bar 603. The torsion bar 603 and the leaf spring 604 suppress the shift of the mirror holder 602 in a Z-axis direction.
In the mirror drive mechanism described in Patent Document 1, stress is concentrated at the elastic pivots 246a-246b and 248a-248b during tilt driving. In the laser pointing device 600 described in Patent Document 2 as well, stress is concentrated at the base portion of the of the torsion bar 603. In order to ensure resistance to such stress, the rigidity of the elastic pivots 246a-246b and 248a-248b or the torsion bar 103 must be enhanced to realize a robust structure, which results in reduced efficiency in tilt drive.
Further, since the mirror drive mechanism described in Patent Document 1 is of a biaxial gimbal structure, the size of the mirror face is large. In the laser pointing device 600 of Patent Document 2 as well, the size of the mirror face is so large due to the arms 606 extending from the mirror holder 602 that the laser pointing device 600 cannot be suitably mounted in a limited space such as in a satellite.
Still further, this kind of beam pointing system is required to have superior vibration characteristics.